These flexible thermoplastic hoses typically have internal bore diameters from ⅛ to ⅝ inch and a length of up to 500 feet. The working pressures in these hoses may be as high, e.g., 1,000 to 10,000 psi working pressures, and the hoses are desired to be light in weight, durable, flexible, abrasion resistant, and have a static discharge.
The high velocity flow of fluids through the hose may create static electricity that could result in static sparking, which may cause fire or explosion, if the hose and equipment are not properly grounded. These hoses are provided with static electricity drains leading to a ground and periodically the electrical resistance of the hose is checked. For example, the end-to-end resistance of the unpressurized hose must not exceed a maximum of 29 megohm and typically the length of hose is limited to 500 feet or less in length. If hose exceeds the 29 megohm resistance, it is to be replaced.
One conventional hose of this kind has a seamless, inner tube or core of nylon and has a carbon conductivity layer encircling the inner tube to act as a static electricity drain. Encircling the carbon conductivity layer is a high tensile synthetic woven fiber layer or tube. An abrasion resistant outer layer is extruded over the woven fiber layer to complete the hose.
Another conventional hose of this kind is formed with an inner core or tube having an internal bore and a first and a second braided yarn filament layer with an electrically conductive tape disposed between the braided layers to conduct static electricity generated by the liquid flowing through the bore in the inner tube or core of the hose. The conductive tape results in a bump or enlargement in the circular cross-section of the hose which provides difficulty when crimping the hose to a metal fitting at an end to conduct the static electricity to ground. For example, the bump may be 0.012 in size.
Another conventional hose of this kind extrudes an electrically conductive tube between the first and second braided layers to conduct static electricity. Typically, the formation of two concentric braided layers involves what is termed a double decking of braiding machines which usually must be attended by a person. In contrast thereto, a single deck or one braiding machine can be usually run unattended without any person in attendance.
There is a need for a new and improved hose of this kind that provides a simple and less expensive static drain than using a metal tape between yarn layers or a conductive, extruded tube between the braided layers.
Also, there is a need for a lighter weight hose of this kind, and a need for a hose of this kind which may be made with an improved method of manufacture.